I’m not sure if a convention has been developed, but if not we need to standardise how sois are named, lest searching become a nightmare.
Most sois have an official numbered name following the road it branches off, and many also have a “regular” traditional name. I understand that current practice is that the numbered name is used in the name field, with other names specified in alt_name.
In Bangkok at least, street signs appear without the word soi in them, e.g.
(Actually that should be one big number shared between both rows.)
It is actually implied or assumed that the reader already knows that the street is a soi. The problem is, there are many ways to say the name. For most roads, it will most often be ซอยพหลโยธิน 40 / Soi พหลโยธิน 40. However, with some roads, it is also common (but not quite more) to hear สุขุมวิทซอย 33 / Sukhumvit Soi 33. I’ve also seen streets tagged with the entire road name + soi number, e.g. ถนนเพชรเกษม ซอย 66 / Thanon Phetchakasem Soi 66. From experience, however, I think this is only done when addressing envelopes. (Personally, I would write it as 123/456 Soi 66, Thanon Phetchakasem, …, but that’s a different matter.) Furthermore, roads which already have a number in their name are an exception to not having the word soi on street signs, e.g. พระรามที่ 6 ซอย 10 / Rama VI Soi 10, but this is due to the need to avoid confusion.
So should it be:
พหลโยธิน 40 / Phahon Yothin 40 - Follow the street signs and leave soi out of the name? I’m not sure if this means incomplete information, but if street signs don’t bother to say soi, why should our maps? This may result in inconsistency though if street signs elsewhere do have the word soi in them.
ซอยพหลโยธิน 40 / Soi Phahon Yothin 40 - Put the word soi at the beginning? This has the benefit of being the most common way the name is actually used in speech and writing.
พหลโยธินซอย 40 / Phahon Yothin Soi 40 - Use the convention of having the road name first? This would avoid inconsistency with Rama VI Soi 10, but for most streets this isn’t the most common way the name is said.
ถนนพหลโยธิน ซอย 40 / Thanon Phahon Yothin Soi 40 - Use the fullest form? As I said above, I don’t think this is actually done when referring to the sois themselves.